Cutter bits having a concave facial surface have been proposed for use in certain mining and agricultural applications. For example, a concave cutter bit mounted on, or attached to, a shank that is rotatably mounted in the bore of a tool holder is shown in U.S. Pat. No. 5,078,219, issued Jan. 7, 1992 to Roger J. Morrell, et al. A significant advantage of such cutting tools is that they are capable of rotation during operation, thereby distributing wear of the cutting edge around the outer peripheral edge of the concave face surface.
However, it has been found that, during operation, dust and small particles of cut material tend to pack around the shank of the concave bits constructed according to the teaching of Morrell, et al. Furthermore, fine particles are forcibly driven into the joint between tool shank and the receiving socket in the tool holder. These problems inhibit the rotation of the tool during cutting operations and prevents even wear distribution about the peripheral edge of the tool.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a concave cutting tool in which the rotary connection between the tool and tool holder is protected against direct penetration of foreign material. It is also desirable to have a concave cutter bit arrangement that has an internal bearing member that further contributes to the free rotation of the cutting tool during operation.